1. Field of the Invention
The present invention generally relates to motor control and more particularly relates to a partitioning of torque and flux currents (Iq, Id) supplied from a DC source when operating a permanent magnet (PM) motor, for example, in a constant power range.
2. Description of the Related Art
The PM synchronous motor possesses many appealing 7 characteristics for various applications, including pure-electric and hybrid-electric vehicles. The maximum input power of a vehicle is dictated by the size of the source (i.e. battery, fuel cell engine, supercapacitor, etc.) and is the product of the DC voltage and DC current. Quite often, the DC bus voltage varies with motor output power (i.e., Torque*Speed). As a result, rapid changes in vehicle load may cause large fluctuations in the DC bus voltage. A traction electric motor drive is often required to perform over a wide operating range. Typically the operating range of an electric machine such as a traction electric motor is divided into two regions: the constant torque region and the constant power region. It is important to maintain the ability to change between both modes of operation quickly and smoothly.
Existing PM motor control, particularly in vehicle applications, performs poorly when the DC bus voltage varies. Rapid fluctuation of the DC bus voltage, for example due to rapidly changing power demands, exacerbates this problem, and existing PM control systems are typically unable to adequately compensate. Fast switching between these two regions requires an improved current regulation methodology and apparatus.